how to define stair-like position to several plane objects?
Via the UI:
Some variation on this one, which has  all  steps in XY plane, and a top-step target vertex set up, ready?

Pivot: 3D cursor, at bottom step
Snap: To: 'Vertex' With: 'Active', and set to affect 'Scale'
Header Options: Affect only Locations

All steps selected, top step active, SCtrlAlt S .. Y to set the axis, Shear the objects' locations a lttle.
Once a regular stagger is achieved, SZ  scale them, with snap, to the target.

I don't think the Shear axes are what they claim to be in the manual, so there may be some playing required. This shear is executed in Global space, Main axis 'Z', Ortho, 'Y'.